Ongoing Struggles With Anxiety or Panic?

I started having these problems about.... last october right after my 20th birthday... or maybe a little before, its kind of .... groggy. Anyway I was driving to school, and i started feeling... Its kind of hard to describe.. basicly like I was about to pass out, like my vision felt spotty, and I started to feel uncomfortable and slowly tightening in my chest. Well lets say that im a little overweight and if your big you feel tightness in your chest, and fainting you think your having a heart attack. Well I finally got to school walked inside sat down, and got really dizzy, I felt the blood rush to my head, and the chest pain kept coming. I swear it felt like rivers of sweat were running from my feet and my forehead. I walked to class, everyone was asking if I was alright, to which I replied I dont know whats happening. I called my nearest family members to come and pick me up from school, which they did and we went to the doctors office. It was a pretty horrible experience.... It was the most scared ive ever been. I eventually gave in and said just end it now, and I calmed down and almost passed out because of exaustion in the car ride home. I felt exhausted for the next couple of days. I hadnt experienced anxiety or any symptoms before that, and nothing triggered it. Now Im having to deal with random anxiety spells and almost panic attacks on a daily basis. I am engaged and living with my amazing fiancee but shes really outgoing, and so was I before this. but now even knowing that its anxiety, when it comes on strong there is this doubt that arises that maybe they or I were wrong, and I have something wrong with my heart, or my artiries are clogged. Each time its like a battle between either resisting and prolonging waiting till its a catagory 5 and giving in, or going to sleep. I dont know what to do. The doctor recently gave me... Lexapro(and anti-depressant / anxiety drug) to try, but its not helping at all, and if anything since taking it I fell really disconnected,and almost in a fog. The symptoms I experience lately are Smothering sensations, chest pains, tightness in throat, head aches, naseau, trouble breathing after eating and some more here and there. At times it comes to a point where I get so fed up that I think its hopeless and Ill never be able to enjoy life, and then my fiancee walks in and makes it feel worth it.... I hope that that lasts though.